The cooling performance of the micro-solid nitrogen spray technique on the cryopreservation vitrification process: A qualitative study

Abstract

The qualitative mechanism of heat transfer during the cooling process by spraying Micro-Solid Nitrogen (MSN2) together with the capability to vitrify a large-volume of samples is experimentally investigated in the article. The experiments were carried out on three samples: one was a 30 30 × 0.1 mm copper plate attached to a 6.75 ml container filled with distilled water, the second was a 25 × 25 × 3 mm ceramic heater with a 15 × 15 × 0.4 mm heat flux sensor installed on top, and the third with a recess of 10 × 10 × 1 mm to test the vitrification capabilities of large-volume biological samples. Thermal characteristic experiments were performed for three initial wall temperatures of 278, 313, and 373 K, respectively. The cooling rate achieved by the MSN2 spray ranges from between 3.97 K/s up to 47 K/s and depends on the specific wall temperature range. The results of the experimental data show an average three times higher value of heat flux by using MSN2 compared to the boiling pool of Liquid Nitrogen (LN2) within the same temperature range. The investigation exposed the second local maximum of heat flux in the wall superheat temperatures between 30 K and 300 K, which is shifted from the Critical Heat Flux (CHF) point towards higher temperatures. The vitrification of the sample was achieved using a cell-free liquid solution with 7 mol/L for both dimethyl sulfoxide (Me2SO) and glycerin agents. The average cooling rate for the vitrified samples during the experiments ranges from between 2 - 4 K/s and is about 3 to 6 times higher than the cooling rate of similar volume samples known from the literature.